Heavy downpour is occurring, yet at which location?
ntv.de: Seems Like Summer's Wrapping Up - Any Chance Left?
Bjoern Alexander: Not until the weekend, at the very least. Instead, we're dealing with some unusual extreme weather conditions.
What's happening here?
On the one hand, a significant winter storm brewing above 1500 meters in the Alps. On the other, substantial rainfall and potential flooding risk for Germany.
Why this sudden weather shift?
Last weekend we saw temps surpassing 30 degrees, but the start of the week brought a sharp drop due to a cold front from Low "Yonca". Now, another cold front from Low Number 2, "Zilan", is coming in: bringing heavy storm winds to the British Isles and causing clashes with the Alps on Wednesday and Thursday night. Meanwhile, another low is forming over Genoa and North Italy, blending cold air from the north with warm, moist air from the overheated Mediterranean.
What are the risks involved?
The main focus is on precipitation, in solid form as snow above 1500 meters. Even in higher valleys down to 1200 to 1300 meters, snowfall could occur with suitable temperatures. So, hikers and skiers, be alert! It could be dangerous. Also, in the layers above 1500 to 2000 meters, substantial new snow accumulations are expected.
How much snow are we looking at?
In the wind shadow areas of the Alps, it could be anywhere from 50 to 100 centimeters - some models even forecast much more. Over 2 meters is not out of the question. Add in lively to stormy winds, snow drifts, and an increased avalanche risk, and we can expect winter-like road conditions on higher roads and passes.
What rainfall amounts should the lower areas prepare for?
Location and intensity are still widely varied in the weather computers' assessments. However, fact is, the low from North Italy will move over the Alps towards the northeast. A so-called Vb situation, which is characterized by extremely heavy rainfall and hard to predict. As of recent calculations, for example, the south and southeast of Germany could have been heavily affected as of Friday. With over 200 liters per square meter, there would be significant flood and overflow risks, even catastrophic ones.
What's the current outlook for Germany?
Until Monday morning, between 60 and 250 liters per square meter could be a possibility, depending on the model. The Berchtesgadener Land, Bavarian Forest, and East Saxony are likely to see the most impact. This would still be a critical to dangerous situation in the worst-case scenario. But most weather models no longer indicate the heaviest rainfall in our region.
Where would the damage be the worst then?
The answer to that question is still uncertain and depends on the future developments of the weather situation.
Current estimates suggest that Austria, the Czech Republic, and Poland would be hit the hardest. In extreme scenarios, models predict 300 to 400 liters per square meter. If this were to occur, the Elbe would also be affected via overflow from the Czech Republic.
Regarding rainfall amounts: How do these figures compare?
Berlin typically gets around 600 to 650 liters per square meter annually, while Cologne averages about 800 liters. During the Ahr Valley flood in July 2021, localized amounts ranged from 100 to 200 liters per square meter. The highest 24-hour rainfall was recorded at Zinnwald-Georgenfeld in Saxony during a Vb weather situation on August 12, 2002, with 312 liters per square meter. This serves as a reminder of these weather conditions' potential and the devastating consequences they can have.
Despite the recent heatwave, Bjoern Alexander predicts that we're not out of the woods yet for summer as we're currently dealing with some unusual extreme weather conditions. The upcoming week is set to bring a significant winter storm in the Alps, accompanied by substantial rainfall and a potential flooding risk for Germany.
